An engine includes a cylinder, a rocker chamber, an air filter, a crankcase and a rocker chamber cover, wherein the rocker chamber cover is disposed above the cylinder. The engine further includes a cover plate, wherein the cover plate is located at the top of the rocker chamber cover, and the rocker chamber cover and the cover plate are spliced to form a separation cavity and a connection channel. According to the engine provided by the invention, the top structure of the rocker chamber is re-designed and the top space of the rocker chamber is sufficiently used so as to achieve the objects of optimizing a lubricating system and reducing emission, as well as reducing the manufacturing cost and difficulty.